Orifice plate for ink jet printer

Abstract: A composite orifice plate for a printer such as a thermal inkjet printer includes a first layer (22) of non-wettable material and a second layer (23) of wettable material joined to the first layer (22). In the orifice plate, nozzle openings (25) extending through the first and second layers (23) allow ink to be ejected through an outlet (26) located on a surface of the first layer (22).

Description: The present invention generally relates to orifice plates for inkjet printers and to processes for manufacture thereof. In practice, the print quality of inkjet printers depends upon the physical characteristics of the nozzles in its printhead. For example, the geometry of a printhead orifice nozzle can affect the size, trajectory, and speed of ink drop ejection. Also, the geometry of a printhead orifice nozzle can affect the ink supply flow to the associated vaporization chamber. Figure 1 shows an example of a conventional inkjet printhead. The illustrated section of the printhead includes a silicon substrate 7, an intermediate polymer barrier layer 9, and an electroplated nozzle plate 11. In the nozzle plate 11, a nozzle orifice 13 is formed having an inlet area 14 and an outlet area 16. It should be understood that a conventional printhead has an array of such nozzle orifices with each nozzle orifice being paired with a vaporization cavity. As further shown in Figure 1, the silicon substrate 7 and the polymer barrier layer 9 together define a vaporization cavity 19 which is in fluid communication with the nozzle orifice 13. The vaporization cavity 19 is sometimes referred to as an ink drop ejection chamber. Further in Figure 1, it should be noted that a dead space 15 is formed where the surface of the barrier layer 9 separates from the converging sidewall 17 that defines the orifice 13 in the electroplated nozzle plate 11. Although such dead spaces are typical in conventional printheads for inkjet printers, they are problematical because they provide sites where static bubbles can be trapped. The trapped bubbles, in turn, can adversely affect the fluid dynamics of ejected drops. It should be understood that, in a conventional inkjet printhead, a heater resistor (not shown in Figure 1) is positioned within each vaporization cavity. Then, all of the heater resistors are connected in a network for selective activation. Also, a conventional printhead includes a channel (not shown in Figure 1) that provides ink flow communication between each vaporization cavity and an ink supply reservoir. In practice, the above-described conventional inkjet printhead has several shortcomings. For instance, conventional inkjet printheads have a metal orifice plate that is inherently wettable and, therefore, provides a surface for ink runout over the outer surface of the orifice plate. The ink runout can cause a condition known as "ink puddling" that may create misdirection and spraying of ink droplets during ejection. On the other hand, it is desirable to have a nozzle orifice with a wettable interior so that the vaporization cavities can be smoothly refilled with ink. EP-A-367541 discloses a composite orifice plate for a printer comprising a first layer of non-wettable material, and a second layer of wettable material. Another shortcoming of the above-described conventional inkjet printhead is that the orifice pates are conventionally formed by plating processes that fix the curvature of the nozzle to have a shape that is like a quarter circle. (The quarter circle shape is shown in cross-section in Figure 1.) The quarter-circle shape is problematical, however, because it is difficult to increase the thickness of a nozzle plate without adversely affecting the architecture of the printhead while still maintaining the quarter-circle shape. Generally speaking, the present invention provides a nozzle plate that reduces the entrapment of static bubbles while combining the benefits of wettable and non-wettable materials and providing easy nozzle architecture design changes. More particularly, the present invention provides a composite orifice plate for a printer, such as a thermal inkjet printer, that includes a first layer of non-wettable material and a second layer of wettable material joined to the first layer. At least one orifice extends through the first layer and at least one opening extends through the second layer. The orifice and opening are in fluid communication and aligned in an axial direction. An ink outlet is located on a surface of the first layer facing away from the second layer and an ink inlet is located on a surface of the second layer facing away from the first layer. Each opening is formed by a converging arcuate side wall, and each orifice is formed by a substantially non-converging sidewall. In accordance with another aspect of the invention, the composite orifice plate includes a first layer of a first material with an orifice extending between opposed surfaces thereof and a second layer of a second material with an opening extending between opposite surfaces thereof. The first and second layers are joined together such that the orifice and the opening are in fluid communication and aligned in an axial direction. The opening is formed by sidewalls which converge towards the orifice and the orifice is formed by substantially non-converging sidewalls. In accordance with a further aspect of the invention, a method of manufacturing a composite orifice plate for a printer such as an inkjet printer is provided which includes coating a layer of polymer material with an adhesion layer, coating a layer of metal on the adhesion layer, providing at least one opening through the layer of metal and providing an orifice through the layer of polymer material. The orifice can be provided by photo-ablating the layer of polymer material using the layer of metal as a mask. A composite orifice plate in accordance with the present invention eliminates problems associated with bubble trappage in conventional inkjet printheads while allowing the nozzle thickness to be easily varied. The present invention can be further understood with reference to the following description of exemplary embodiments thereof in conjunction with the appended drawings, wherein like elements are provided with the same reference numerals. In the drawings: Figure 1 shows a cross-sectional view, to an enlarged scale, of a conventional orifice plate. Figure 2 is a cross-sectional view of a composite orifice plate in accordance with the present invention. It should be understood that, in practice, a composite orifice plate includes a plurality of orifices, only one of which is shown in the drawing. Figure 3 is a cross-sectional view of a composite orifice plate in accordance with the present invention, showing an intermediate stage of production. As shown in Figure 2, a composite orifice plate according to the present invention includes a first layer 22 of a non-wettable material and a second layer 23 of a wettable material. A plurality of orifices 24, only one of which is shown in the drawing, is formed through the first layer 22. Also, a plurality of openings 25, only one of which is shown in the drawing, is formed through the second layer 23 such that each opening of the plurality is aligned in fluid flow communication with a corresponding one of the orifices 24 such that each pair of orifices 24 and openings 25 form a nozzle that has an outlet 26 on the outer surface of the first layer 22, and an inlet 30 on a surface of the second layer 23 facing away from the first layer 22. The orifices 24 and the openings 25 normally are circular in plan view and are symmetric about their vertical axis. Preferably, the first layer 22 in the composite orifice plate of the present invention is a non-wettable polymer material such as a polyimide film, like "KAPTON"(TM) or "UPILEX."(TM) The wettable second layer 23 preferably is formed of a metal material, such as nickel, that is more wettable than the first layer 22. Accordingly, the composite orifice plate has a non-wettable outer surface and a wettable (e.g., metallic) inner nozzle surface. The first layer 22 normally is at least twice as thick as the second layer 23 and, together, the two layers usually are about 50.8 µm (two mils) thick. It should be noted that, as shown in Figure 2, the orifices 24 in the first layer 22 have a non-converging sidewall 20. By way of contrast, the openings 25 in the second layer 23 have an arcuate sidewalls 21. Preferably, the arcuately converging sidewall 21 has a radius of curvature (designated by the letter " R " in Figure 2) which approximates to the total thickness of the second layer 23. It should also be noted in Figure 2 that a barrier layer 28 of polymer material is mounted to the second layer 23 on its side opposite the first layer 22 and that a silicon substrate 29 is mounted to the opposite side of the barrier layer 28. To the extent that a dead space 40 is created where the surface of the barrier layer 28 separates from the converging sidewall 21 of the second layer 23, the deleterious effects of the dead space can be minimized by forming the second layer 23 sufficiently thin that the dead space 40 is too small to trap bubbles. By using such a design, energy losses of ejected ink drops due to entrapped static bubbles in the dead spaces are minimized. Thus, it can be appreciated that the above-described composite orifice plate eliminates problems associated with the above-described dead space while allowing the nozzle thickness to be easily varied. Various methods can be used to form the composite orifice plate of the present invention. For example, during fabrication, one side of the polymer material of first layer 22 can be coated with an adhesion or seed layer 32 as shown in Figure 3. The adhesion layer 32 can be, for example, a sputter-deposited layer of metal such as chromium or TaAl, or a combination thereof. The adhesion layer 32 can be patterned with photoresist so that the orifices 24 can be etched. In that case, the metallic second layer 23 is electroplated onto the adhesion layer 32 and built up to have the above-described arcuate converging walls 21 (Figure 2) that form the openings 25 in the second layer. When constructed as described above, the metal of second layer 23 can serve as a mask for photo-ablation. More particularly, the orifices 24 in the first layer can be photo-ablated through the polymer material by exposing the layer of metal of the second layer 23 to a beam of laser energy that passes into the first layer 22 of polymer material via the openings 25. After the orifices 24 are formed, the metal of the second layer 23 can be plasma etched to remove any soot formed by the photo-ablation step and render it wettable. Alternatively, the composite orifice plate of the present invention can be manufactured from a polymer/metal composite material. In that case, the metal of the second layer 23 is patterned as a mask for laser ablation of the polymer material of the first layer 22. Following ablation, the metal of the second layer 23 can be plasma etched to remove soot and render it wettable. In one particular process, the composite orifice plate is manufactured by coating a first layer 22 of polymer material with an adhesion layer 32. Patterns of a photoresist material, with lateral dimensions corresponding to those of the orifices 24, are formed on top of the adhesion layer 32. Then, the metal of the second layer 23 is electroplated. After electroplating, the photoresist material is removed, exposing areas of the adhesion layer that define the openings 25 for the orifices 24. Thereafter, the metal of the second layer 23 is used as a mask. With such a mask, the exposed areas of the adhesion layer 32 is etched off, and the orifices 24 are formed by photo-ablation through the first layer 22 of polymer material with a beam of laser energy radiating onto the second layer 23. In an alternative process for manufacturing the above-described composite orifice plate, the polymer material of the first layer 22 is coated by an adhesion layer 32 and is patterned with a photoresist material. The pattern defined by the photoresist material has areas of the adhesion layer 32 exposed, the areas having lateral dimensions corresponding to the orifices 24. The exposed adhesion layer 32 is etched. Then the photoresist material is removed, and the second layer 23 is formed on the adhesion layer 32, as shown in Figure 3. Next, the orifices 24 are formed by photo-ablation of the polymer material using the metal of the second layer 23 as a mask. In yet another alternative process for manufacturing the above-described composite orifice plate, the metal comprising the second layer 23 is continuous and the openings 25 are formed by coating a layer of photoresist material onto the metal. In this case, the photoresist material is provided in a pattern that includes at least one open region whose size corresponds to the lateral dimensions of each of the orifices 24 in the polymer material of the first layer 22. The layer of metal comprising the second layer 23 is then etched through the open region in the photoresist material to provide the openings 25. After etching, the photoresist material is removed and, then, the metal layer is used as a mask for photo-ablation of the orifices 24 in the polymer material of first layer 22. The foregoing has described the principle preferred embodiments and modes of operation of the present invention. However, the invention should not be construed as being limited to the particular embodiments discussed. Thus, the above-described embodiments should be regarded as illustrative rather than restrictive and it should be appreciated that variations may be made in those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims: A composite orifice plate for a printer such as a thermal inkjet printer, comprising: a first layer (22) of non-wettable material; a second layer (23) of wettable material joined to the first layer (22); and at least one orifice (24) extending through the first layer (22) and at least one opening (25) extending through the second layer (23), the orifice (24) and the opening (25) being in fluid communication and aligned in an axial direction with an ink outlet (26) located on a surface of the first layer (22) facing away from the second layer (23) and an ink inlet (30) located on a surface of the second layer (23) facing away from the first layer (22), characterised in that: each of the openings (25) is formed by an arcuate sidewall (21) that converges towards the orifice (24), and each of the orifices (24) is formed by a substantially non-converging sidewall (20). A composite orifice plate according to Claim 1, wherein the radius of curvature of the arcuate sidewall (21) is about equal to a maximum thickness of the second layer (23). A composite orifice plate according to Claim 1 or 2, wherein the first layer (22) comprises a polymer material and the second layer (23) comprises a metal. A composite orifice plate according to any preceding Claim, further comprising a barrier layer (28) and a silicon substrate (29) adjacent to the second layer (23), the barrier layer (28) having a surface that separates from the converging sidewall (21) of the second layer (23) by a dead space (40) that is small enough to not trap static bubbles. A method of manufacturing a composite orifice plate for a printer such as an inkjet printer, comprising: coating a layer of polymer material with an adhesion layer; coating a layer of metal on the adhesion layer; providing at least one opening (25) through the layer of metal; characterised in that: it provides at least one non-converging orifice (24) in the layer of polymer material such that each orifice (24) is in fluid communication and aligned in an axial direction with converging opening (25) formed by an arcuate sidewall (21) in the layer of metal. A method according to Claim 5, further comprising coating a layer of a photoresist material on the adhesion layer prior to coating the layer of metal on the adhesion layer, the photoresist material being provided in a pattern that includes at least one region corresponding in size to dimensions of the orifice (24) in the layer of polymer material, the opening (25) in the layer of metal being provided by electroplating the layer of metal on the adhesion layer, the method further including removing the photoresist material after the layer of metal is plated on the adhesion layer but before the orifice (24) is provided in the layer of polymer material. A method according to Claim 5, wherein the opening (25) in the layer of metal is provided by coating a layer of photoresist material on the layer of metal, the photoresist material being provided in a pattern that includes at least one open region corresponding in size to dimensions of the orifice (24) in the layer of polymer material, the method further including etching the layer of metal through the open region in the photoresist material so as to provide the opening (25) in the layer of metal followed by removing the photoresist material from the layer of metal. A method according to Claim 5, wherein the orifice (24) is formed by photo-ablation with a laser by using the layer of metal as a mask such that a beam of laser energy passes through the opening (25) in the layer of metal and into the layer of polymer material.

Inventors: PAN ALFRED I, TAPPON ELLEN R, PAN, ALFRED I., TAPPON, ELLEN R.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1994
Main classification: B41J2
IPC codes: B41J2